1. Field of the Invention
This invention relates to a focusing screen mounting device in a camera, and in particular to a removable focusing screen mounting device in a single lens reflex camera.
2. Related Background Art
The focusing screen of a single lens reflex camera is usually provided below the pentaprism of a finder optical system. Cameras designed to permit the focusing screen to be interchanged with another are known. There are two types of techniques for removing the focusing screen, i.e., the type in which the pentaprism is removed upwardly and then the focusing screen is pulled out upwardly, and the type in which the pentaprism is not moved but the focusing screen is moved downwardly into a mirror box and then is removed. The former type is simple in construction, but all parts are received from above into the camera housing and therefore, where dust or the like has entered the space between the underside of the pentaprism and the focusing screen, it is impossible to clean the pentaprism unless it is removed. Also, where it is desired to interchange the focusing screen with another type of focusing screen, the pentaprism must likewise be removed and thus, the interchange is cumbersome and inconvenient. Further, along with the recent tendency of cameras toward the utilization of electronics, it is often the case that various electronic parts are disposed on the upper surface of the pentaprism, and to remove the pentaprism, it is necessary to remove such electronic parts at the same time, and the removal thereof requires much time.
On the other hand, the latter type is designed as shown, for example, in FIG. 7 of the accompanying drawings. In this Figure, a pentaprism 1 and a field frame 5 are provided in a prism box 3 fixed to a camera housing 4, and a focusing screen 2 is supported in such a manner as to be urged against the lower end surface 13a of the prism box 3 by a holding frame 6 through a plate spring 7. The right end of the holding frame 6 is rotatably supported by a shaft pin 8, and the left end of the holding frame 6 is designed to be engaged by an engaging pawl 9. Accordingly, by pulling the engaging pawl 9 in the direction of the arrow, the holding frame 6 is rotatively displaced downwardly, whereby the focusing screen 2 can be removed.
In this latter type, however, the parts such as the holding frame 6 and the engaging pawl 9 are required, and this leads to an increased cost and also, the space for providing said parts therein has impeded the compactness of the camera.